Transmission for a road vehicle with hybrid propulsion

ABSTRACT

Transmission for a road vehicle with hybrid propulsion; the transmission comprises: a gearbox provided with one primary shaft, one secondary shaft and at least one pump actuated by an activating shaft; at least one clutch connected to the primary shaft and presenting a part which is normally conductive which can be connected to a drive shaft of a thermal engine; at least one reversible electric machine presenting a shaft mechanically connectable to the primary shaft; a first mechanical transmission which transmits motion from the normally conductive part of the clutch to the activating shaft; and a second mechanical transmission which transmits motion from the shaft of the electric machine to the activating shaft.

RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. Section 119 to Italian Patent Application Serial No. B02009A 000465, filed on Jul. 21, 2009, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a transmission for a road vehicle with hybrid propulsion.

BACKGROUND

A hybrid vehicle comprises an internal combustion thermal engine, which transmits torque to the driving wheels by means of a transmission provided with a gearbox coupled with a clutch, and at least one electric machine, which is electrically connected to an electric accumulation system, and mechanically connected to the driving wheels.

The following is possible while traveling: either a thermal operating mode, in which the torque is generated only by the thermal engine and the electric machine may work as generator for recharging the electric accumulation system; or an electric operating mode, in which the thermal engine is off and the torque is generated only by the electric machine working as motor; or a combined operating mode, in which the torque is generated both by the thermal engine and by the electric machine working as motor. Furthermore, in order to increase overall energy efficiency during all steps of decelerating, the electric machine may be used as generator for a regenerative deceleration in which the kinetic energy possessed by the vehicle is partially converted into electric energy, which is stored in the electric accumulation system instead of being fully dissipated in frictions.

On some hybrid vehicles, the gearbox comprises a circulation pump for circulating lubricating oil through the gears of the gearbox so as to ensure adequate lubrication of the gears themselves. Furthermore, in the case of a hydraulically actuated automatic manual transmission (commonly named “AMT”), the gearbox further comprises an actuation pump which supplies the hydraulic pressure needed for hydraulic gear engagement and selection and clutch operation.

In the currently manufactured gearboxes, the gearbox pumps are actuated by an auxiliary activating shaft, which takes motion from the drive shaft (possibly with the interposition of a transmission shaft), i.e. upstream of the clutch, so that it is always actuated when the clutch is open. This condition makes the mechanical connection of an electric machine to a shaft of the gearbox less convenient, because in case of electric traction (i.e. when the thermal engine is off), the clutch must remain closed to actuate the pumps and therefore the thermal engine is also rotably fed (with considerable frictions and inertia). Furthermore, because the electric machine cannot be rotated when disconnected from the thermal engine (in these conditions there would be no lubrication of the gearbox and, above all, no hydraulic pressure needed to actuate the clutch), the electric machine cannot be used as starter motor of the thermal engine, because in order to use the electric machine as starter motor of thermal engine the electric machine must be rotated at high speed before connecting the electric machine to the thermal engine in order to make the electric machine accumulate a high amount of kinetic energy.

In order to solve the problem described above, it has been suggested to make the activating shaft of the pumps of the gearbox mechanically independent from the drive shaft, and to actuate the pump activating shaft by means of a dedicated motor; however, this solution normally requires re-designing the gearbox, with high development costs and little efficiency from the energy point of view, because when the thermal engine is running (i.e. for most time of use of the vehicle), it is more efficient to use part of the torque generated by the thermal engine to directly actuate the auxiliaries rather than converting part of the torque generated by the thermal engine into electricity, which is transformed back into mechanical torque by an electric motor. Furthermore, arranging an electric motor mechanically coupled to the activating shaft of the gearbox pumps is not easy, because the space in the gearbox area is small, it is rather hot by effect of the heat generated by friction inside the clutch and the gearbox, and is not very ventilated because it is normally in the middle of the vehicle.

Patent application US2008087487A1 describes a transmission for a road vehicle with hybrid propulsion comprising: a double clutch gearbox provided with two primary shafts, a secondary shaft, and a lubrication pump; two clutches connected to the primary shafts and comprising a normally conductive part, which can be connected to a drive shaft of a thermal engine; and a reversible electric machine comprising a shaft mechanically connectable to one of the two primary shafts; a first mechanical transmission, which transmits motion from the normally conductive part of the clutch to the lubrication pump and comprises a first freewheel; and second mechanical transmission which transmits motion from the shaft of the electric machine to the lubrication pump and comprises a second freewheel.

SUMMARY

Some of the disclosed examples provide a transmission for a road vehicle with hybrid propulsion, which is free from the above-described drawbacks and being, at the same time, easy and cost-effective to manufacture.

According to various examples, a transmission for a road vehicle with hybrid propulsion is made as disclosed in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which set forth some non-limitative embodiments thereof, in which:

FIG. 1 is a diagrammatic view of a road vehicle with hybrid propulsion;

FIG. 2 is a diagrammatic view of a transmission of the road vehicle in FIG. 1, made in accordance with some examples;

FIG. 3 is a side, diagrammatic view with parts removed for clarity of an activating shaft of the transmission in FIG. 2;

FIG. 4 is a diagrammatic view of a further embodiment of a transmission of the road vehicle in FIG. 1 made in accordance with some examples;

FIG. 5 is a diagrammatic view of the mechanical connections of an electric machine of the transmission in FIG. 4;

FIG. 6 is a diagrammatic view of a cooling and lubricant circuit of the electric machine in FIG. 5;

FIG. 7 is a diagrammatic view of further part of a cooling and lubricant circuit of FIG. 6;

FIG. 8 is a side, diagrammatic view with parts removed for clarity of an activating shaft of the transmission in FIG. 4;

FIGS. 9 and 10 show two diagrammatic plan views, with parts removed for clarity, of the machine in FIG. 5; and

FIG. 11 is a diagrammatic electric propulsion power circuit of the road vehicle in FIG. 1.

DETAILED DESCRIPTION

In FIG. 1, numeral 1 indicates as a whole a road vehicle with hybrid propulsion provided with two front wheels 2 and two rear driving wheels 3, which receive torque from a hybrid propulsion system 4.

The hybrid propulsion system 4 comprises an internal combustion engine 5, which is arranged in frontal position and is provided with a drive shaft 6, an automatic manual transmission 7 (commonly named “AMT”), which transmits the torque generated by the internal combustion engine 5 to the rear drive wheels 3, and a reversible electric machine 8 (i.e. an electric machine which can work either as electric motor, using electricity and generating mechanical torque, or as an electric generator, using mechanical energy and generating electricity), which is mechanically connected to the transmission 7.

The transmission 7 comprises a transmission shaft 9 which on one end is angularly integral with the drive shaft 6 and on the other end is mechanically connected to a double clutch gearbox 10, which is arranged in rear position and transmits motion to the rear driving wheels 3 by means of two axles shafts 11, which receive motion from a differential 12. The reversible electric machine 8 is mechanically connected to the double clutch gearbox 10, as described in greater detail below, and is piloted by an electronic power converter 13 connected to an electric accumulation system 14, which is adapted to store electricity, and is provided with chemical batteries and/or supercapacitors.

As shown in FIG. 2, the double clutch gearbox 10 comprises two mutually coaxial, independent primary shafts 15 and 16, inserted within one another, and two coaxial clutches 17 and 18 arranged in series, each of which is adapted to connect a respective primary shaft 15 or 16 to the transmission shaft 9 (and thus to the drive shaft 6 of the thermal internal combustion engine 5). Furthermore, the double clutch gearbox 10 comprises two secondary shafts 19 and 20, which are both angularly integral with the input of the differential 11, which transmits motion to the rear drive wheels 3.

The double clutch gearbox 10 shown in the FIG. 2 has seven forward gears indicated by Roman numerals (first gear I, second gear II, third gear III, fourth gear IV, fifth gear V, sixth gear VI and seventh gear VII) and one reverse gear (indicated by the letter R). The primary shafts 15 and 16 are mechanically coupled to the secondary shafts 19 and 20 by means of a plurality of gear pairs 21, each of which defines a respective speed, and comprises a primary gear mounted on a primary shaft 15 or 16 and a secondary gear, which is mounted on a secondary shaft 19 or 20 and constantly meshes with the primary gear. In order to allow the correct operation of the double clutch gearbox 10, all the odd gears (first gear I, third gear III, fifth gear V, seventh gear VII) are coupled to a same primary shaft 15, while all the even gears (second gear II, fourth gear IV, and sixth gear VI) are coupled to the other primary shaft 16.

Each primary gear 8 is keyed onto a respective primary shaft 15 or 16 to rotate, again integrally, with the primary shaft 15 or 16 itself, and permanently meshes with the respective secondary gear; instead, each secondary gear is idly mounted on the respective secondary shaft 19 or 20. The double clutch gearbox 10 comprises for each couple 21 of gears a respective synchronizer 22, which is mounted coaxially to respective secondary shaft 19 or 20, and is adapted to be actuated to engage the respective secondary gear 19 or 20 (i.e. to make the respective gear angularly integral with the secondary shaft 19 or 20).

The electric machine 8 has a drive shaft 23, which is permanently connected to the primary shaft 15 so as to rotate again integrally with the primary shaft 15 itself. According to certain examples, starting from an existing double clutch gearbox casing 10 not initially designed for hybrid traction, the primary shaft 15 is elongated on the side opposite to the clutches 17 and 18 so as to protrude from a gearbox casing 24; therefore, outside the gearbox 24, the primary shaft 15 is made angularly integral (e.g. by butt jointing) to the shaft 23 of the electric motor 8.

Reference is made to patent application IT2008B000594 incorporated herein by reference in its entirety for a description of the operating mode of the electric machine 8.

The double clutch gearbox 10 comprises a circulation pump 25 for circulating lubricating oil through the gears of the gearbox 10 and ensure adequate lubrication of the gears themselves. Furthermore, the double clutch gearbox 10 comprises an actuating pump 26 which provides the hydraulic pressure needed to operate the hydraulic engagement actuators of the gears (e.g. of the actuators of the synchronizers 22) and of the control actuators of the clutches 17 and 18.

The two pumps 25 and 26 of the gearbox 10 are actuated by an through auxiliary activating shaft 27 (i.e. which passes through each pump 25 and 26), which on one side takes motion, by means of a mechanical transmission 28, from a front basket 29 of the clutches 17 and 18, which is integral (with the drive shaft 6 with the interposition of the transmission shaft 9) and on the opposite side, takes motion, by means of a mechanical transmission 30, from the primary shaft 15, which is integral with the shaft 23 of the electric machine 8. The front basket 29 constitutes the normally conductive (i.e., transmissive) part of the clutches 17 and 18, because it receives motion from the thermal engine 5 and transmits it to the normally conductive parts (i.e. the hubs of the clutches 17 and 18) integral with the primary shafts 15 and 16.

The mechanical transmission 28 includes a cascade of gears and is provided with a freewheel 31 (or idle wheel 31), which transmits motion (i.e. meshes) when it rotates in a certain direction and does not transmit motion (i.e. does not mesh) when it rotates in the opposite direction. Similarly, the mechanical transmission 30 also includes a cascade of gears and is provided with a freewheel 32 (or idle gear 32), which transmits motion (i.e. meshes) when it rotates in a certain direction and does not transmit motion (i.e. does not mesh) when it rotates in the opposite direction. The meshing direction of the freewheel 32 of the mechanical transmission 30 is opposite to that of the freewheel 31 of the mechanical transmission 28: in other words, freewheel 32 transmits motion (i.e. meshes) when it rotates in a given direction, while freewheel 31 transmits motion (i.e. meshes) when it rotates in the opposite direction.

Finally, the gear ratio determined by the mechanical transmission 28 is higher than the gear ratio determined by the mechanical transmission 30, so that the mechanical transmission 28 makes the activating shaft 27 rotate faster than the mechanical transmission 30, the input speed being equal.

According to a possible embodiment, a disengagement sleeve 33 is located along the activating shaft 27 and upstream of the second mechanical transmission 32 and fulfils the function of allowing the portion of the activating shaft 27 arranged on the right of the disengagement sleeve 33 to slide axially with respect to the portion of the activating shaft 27 arranged on the left of the disengagement sleeve 33. The objective of the disengagement sleeve 33 is to allow axial adjustments of the position of the mechanical transmission 32 (typically to recover constructive assembly tolerance) without affecting the pumps 25 and 26 of the gearbox 10 and the mechanical transmission 30.

As shown in FIG. 3, the mechanical transmission 28 consists of a cascade of gears and comprises a gear 34 integral with the front basket 29 and a gear 35, which meshes the gear 34 and is connected to the activating shaft 27 by means of the freewheel 31; in particular, the freewheel 31 is integrated in the gear 35, i.e. forms the gear hub 35. Similarly, the mechanical transmission 30 consists of a cascade of gears and comprises a gear 36 integral with the primary shaft 15 and a gear 37, which meshes the gear 36 and is connected to the activating shaft 27 by means of the freewheel 32; in particular, the freewheel 32 is integrated in the gear 37, i.e. constitutes the hub of the gear 37.

The operation of the transmission 7 is described below with reference to the pumps 25 and 26 of the gearbox 10.

When the rotation speed imposed by the activating shaft 27 of the mechanical shaft 28 (and thus of the drive shaft 6 of the thermal engine 5) is higher than the rotation speed imposed by the activating shaft 27 of the mechanical transmission 30 (and thus of the primary shaft 15 integral with the electric machine 8), then the freewheel 31 is meshed and thus transmits motion towards the pumps 25 and 26 of the gearbox 10, while the freewheel 32 is not meshed and thus does not transmit motion towards the pumps 25 and 26 of the gearbox 10; in other words, the activating shaft 27 is rotated by the drive shaft 6 of the thermal engine 5, while the activating shaft 27 is isolated from the primary shaft 15 integral with the electric machine 8.

When the rotation speed imposed by the activating shaft 27 of the mechanical shaft 28 (and thus of the drive shaft 6 of the thermal engine 5) is higher than the rotation speed imposed by the activating shaft 27 of the mechanical transmission 30 (and thus of the primary shaft 15 integral with the electric machine 8), then the freewheel 32 is meshed and thus transmits motion towards the pumps 25 and 26 of the gearbox 10, while the freewheel 31 is not meshed and thus does not transmit motion towards the pumps 25 and 26 of the gearbox 10; in other words, the activating shaft 27 is rotated by the primary shaft 15 integral with the electric machine 8, while the activating shaft 27 is isolated from the drive shaft 6 of the thermal engine 5.

In use, when the thermal engine 5 is on, i.e. when the drive shaft 6 of the thermal engine 5 rotates, and one of the clutches 17 and 18 is closed, the rotation speed imposed by the activating shaft 27 of the mechanical transmission 28 (and thus of the drive shaft 6 of the thermal engine 5) is always higher than the rotation speed imposed by the activating shaft 27 of the mechanical transmission 30 (and thus of the primary shaft 15 integral with the electric machine 8), because the transmission ratio determined by the mechanical transmission 28 is higher than the transmission ratio determined by the mechanical transmission 30 so that, the input speed being equal, the mechanical transmission 28 makes the activating shaft 27 rotate faster than the mechanical transmission 30. In this situation, the activating shaft 27 is rotated by the drive shaft 6 of the thermal engine 5.

When the thermal engine 5 is on, i.e. the drive shaft 6 of the terminal engine 5 rotates, and the clutch 17 and 18 are both open, the activating shaft 27 may be rotated either by the drive shaft 6 of the thermal engine 5 or by the primary shaft 15 integral with the electric machine 8 according to the rotation speed of the shaft 23 of the electric machine 8 (i.e. the primary shaft 15 of the gearbox). Indeed, when both clutches 17 and 18 are open, the rotation speed of the primary shaft 15 of the gearbox is entirely separate from the rotation speed of the drive shaft 6 of the thermal engine 5. In all cases, when the thermal engine 5 is on, the activating shaft 27 is rotated by the drive shaft 6 of the thermal engine 5; generally, when the thermal engine 5 is on, the activating shaft 27 is rotated by the primary shaft 15 integral with the electric machine 8 only in case of regenerative braking when the electric machine 8 is operated as generator to recover kinetic energy of the vehicle 1.

When the thermal engine 5 is off, i.e. the drive shaft 6 of the thermal engine 5 is off, and the shaft 23 of the electric machine 8 (and thus in case of rotation of the primary shaft 15) rotated at the rotation speed imposed by the activating shaft 27 of the mechanical transmission 28 (thus of the drive shaft 6 of the thermal engine 5) is always lower than the rotation speed imposed by the activating shaft 27 of the mechanical transmission 30 (i.e. of the primary shaft integral with the electric machine 8). In this situation, the activating shaft 27 is rotated by the primary shaft 15 integral with the electric motor 8.

When the thermal engine 5 is off, i.e. the drive shaft 6 of the thermal engine 5 is stopped, and the shaft 23 of the electric machine 8 is stopped, then the activating shaft 27 is also stopped.

As shown in FIG. 2, the gearbox 10 comprises a reverse R, which receives motion from the primary shaft 16; thus, the reverse movement of the vehicle 1 is made by means of the gearbox 10 exploiting the torque generated by the internal combustion engine 5. According to a different embodiment (not shown), the gearbox 10 made be free from reverse R, which is replaced by a further forward gear (in this case, an eighth gear VIII) and the reverse movement of the vehicle 1 is obtained by exploiting the electric machine 8; in other words, the electric machine 8 is operated as engine with direction of rotation opposite to the usual one to apply a torque to the rear drive wheels 3 which pushes the vehicle 1 in reverse. In this embodiment, the gearbox 10 may have an additional forward gear without any increase of construction complication (instead, with a simplification, because the idle gear of reverse R is missing), exploiting the versatility of the electric machine 8, which may rotate indifferently in the two directions.

A limit to the embodiment of the transmission 7 shown in FIGS. 2 and 3 consists in that the electric machine 8 is used to make the reverse movement of the vehicle 1, the electric machine 8 is not capable of rotating the activating shaft 27 (and thus the pumps 25 and 26 of the gearbox) by effect of the presence of the freewheel 32 in the mechanical transmission 30. Consequently, if the electric machine 8 is used to obtain the reverse movement of the vehicle 1, the actuating pump 26, which provides the hydraulic pressure necessary for operation of the hydraulic engagement actuators of the gears (i.e. of the actuators of the synchronizers 22) and of the control actuators of the clutches 17 and 18, cannot work; in this situation, in order to avoid the operative blocking of the hydraulic actuators, a hydraulic accumulator of considerable size must be contemplated in the hydraulic circuit of the actuating pump 26. However, it is not simple to find an adequate space to contain such hydraulic accumulator of considerable size in proximity of the gearbox 10.

The alternative embodiment of the transmission 7 shown in FIG. 4 has been suggested in order to solve the aforesaid problem.

The transmission 7 shown in FIG. 4 differs from the transmission 7 shown in FIG. 2, because in the transmission 7 shown in FIG. 4 the shaft 23 of the electric machine 8 is not permanently connected to the primary shaft 15 of the gearbox 10 (as shown in the transmission 7 shown in FIG. 2), but instead the shaft 23 of the electric machine 8 connects the primary shaft 15 to the gearbox 10 in separable (i.e. disengageable) manner by means of an electrically controllable connecting device 38. Thus, by acting on the connecting device 38, either the shaft 23 of the electric machine 8 can be connected to the primary shaft 15 of the gearbox 10 or the shaft 23 of the electric machine 8 can be separated from the primary shaft 15 of the gearbox 10. According to some examples, the connecting device 38 consists of an electromagnetic “dog clutch”, which does not allow a relative sliding between the shaft 23 of the electric machine 8 and the primary shaft 15 of the gearbox 10, and is described more in detail below.

By virtue of the presence of the connecting device 38, the shaft 23 can be disconnected from the electric machine 8 of the primary shaft 15 of the gearbox 10 when necessary to obtain the operating mode that would not be possible in the embodiment of the transmission 7 shown in FIG. 2.

In this embodiment, the mechanical transmission 30 connects the activating shaft 27 of the shaft 23 of the electric machine 8, therefore the connecting device 38 is arranged downstream of the mechanical transmission 30 with respect to the electric machine 8.

As shown in FIG. 5, the shaft 23 of the electric machine 8 is rotationally mounted about a rotation axis 39, which is also in common with the primary shaft 15 (i.e. the shaft 23 of the electric machine 8 is coaxial with the primary shaft 15). Furthermore, the shaft 23 of the electric machine 8 has a tubular shape and centrally displays a pass-through cavity. A connecting shaft 40 is arranged in the central pass-through cavity of the shaft 23 in the electric machine 8, which shaft is rotationally mounted about the rotation axis 39 and constitutes an extension of the primary shaft 15 to which the head is jointed by means of a coupling 41. The connecting shaft 40 crosses side to side the whole shaft 23 of the electric machine 8 and from a side opposite to the shaft 15 is joinable to the shaft 23 by means of connecting device 38. In other words, the connecting device 38 is arranged on the opposite side of the electric machine 8 with respect to the primary shaft and receives motion from the primary shaft 15 by means of the connecting shaft 40, which is arranged inside the shaft 23 of the electric machine 8 and crossing the whole shaft 23 itself side to side.

The connecting device 38 comprises a gear 42 with straight teeth integral with the connecting shaft 40, a gear 43 with straight teeth integral with the shaft 23 and arranged parallel and facing the gear 42, a toothed sleeve 44 carried by the gear 42 and mounted in axially mobile manner, and an electromagnetic actuator device 55, which is adapted to axially move the sleeve 44 between a coupling position and a decoupling position (shown in FIG. 5), in which the sleeve 44 does not mesh the gear 43, and a coupling position (not shown), wherein the sleeve 44 meshes with the gear 43 to make the gear 43 the same angularly integral with the gear 42.

In order to move the sleeve 44 from the decoupling position to the coupling position, i.e. to make the gear 42 which rotates with the primary shaft 15 integral with the gear 43 which rotates with the shaft 23 of the electric machine 8, the two gears 42 and 43 must necessarily be synchronous, i.e. rotating at essentially the same speed. Consequently, in order to be able to move the sleeve 44 from the decoupling position to the coupling position the electric machine 8 must be piloted to follow the rotation of the primary shaft 15 (i.e. of the connecting shaft 40); for this purpose, an encoder 46 is provided, which in real time detects the angular position of the primary shaft 15 (i.e. of the connecting shaft 40) and an encoder 47, which detects in real time the angular position of the shaft 23 of the electric machine 8: by exploiting the measurements provided by two encoders 46 and 47, the electric machine 8 can be piloted to synchronize the rotation of the two gears 42 and 43, so as to allow the engagement of the sleeve 44 on the gear 43. According to some examples, the encoder 46 is integral with the gear 42 and is arranged on the opposite side with respect to the connecting shaft 40.

The electric machine 8 comprises a cylindrical rotor 48, which is carried by the shaft 23 to rotate about the rotation axis 39, and a cylindrical stator 49, which is arranged in fixed position about the rotor 48. The rotor 48 directly supports the gear 36 of the mechanical transmission 30; in this embodiment, the gear 36 is cup-shaped, overhanging protrudes from one side of the rotor 48, and has external teeth so as to mesh with the teeth of the other gear 37 belonging to the mechanical transmission 30. The gear 37 which meshes with the gear 36 is connected to the activating shaft 27 by means of the freewheel 32; in particular, the freewheel 32 is integrated in the gear 37, i.e. constitutes the hub of the gear 37, and transmits motion to a connecting shaft 50, which is butt jointed to the activating shaft 27. In some examples, the connecting shaft 50 is connected to the activating shaft 27 by means of an Oldham coupling 51 (or, alternatively, a Schmidt coupling 51) which allows a given offsetting between the two shafts 27 and 50 themselves; the function of the Oldham coupling 51 is to compensate inevitable manufacturing tolerances avoiding to generate mechanical strain deriving from imperfect alignment between the two shafts 27 and 50. The electric machine 8 is centered with respect to the primary shaft 15 (i.e. perfect coaxiality between the shafts 15 and 40 is sought when mounting the electric machine 8); consequently, all constructive tolerances are discharged on the coupling between the shafts 27 and 50, which can thus present imperfect coaxiality and such misalignments are absorbed and compensated by the Oldham coupling 51.

According to some examples, the encoder 47 reads the angular position of the crown of the gear 37 (which permanently meshes the gear 36 and thus is angularly integral with the rotor 48 and the shaft 23 of the electric machine 8); in particular, the crown of the gear 37 supports a cup-shaped element 52, which overhanging protrudes from one side of gear 37 itself and is coupled to the encoder 47.

According to some examples, the connecting shaft 40 in proximity to the coupling 41 has a weakened zone 53, which is destined to fracture, determining a controlled breakage in case of excessive overload. In other words, in case of control error of the electric machine 8, very high intensity anomalous torques may appear between primary shaft 15 of the gearbox 10 and the shaft 23 of the electric machine 8, which torques could determine the mechanical destruction of the gearbox 10 and/or of the electric machine 8; in order to avoid damaging the gearbox 10 and/or the electric machine 8, a weakened zone 53 is created, which breaks when the torque acting on the connecting shaft 40 is too high (i.e. exceeds a maximum value established during the step of designing). The replacement of the connecting shaft 40 after breakage in the weakened zone 53 is relatively simple and fast, because it is possible to axially remove the connecting shaft 40 from the electric machine 8 by the connecting device 38 after having opened the coupling 41 (obviously after having preventively removed the connecting device 38).

The gear 37 (which permanently meshes with the gear 36 and thus is angularly integral with the rotor 48 and the shaft 23 of the electric machine 8) also rotates a circulation pump 54, by means of a cascade of gears (not shown), which pump is part of a cooling and lubrication circuit 55 of the electric machine 8 (shown in FIG. 6), which will be described below.

The electric machine 8 comprise a box 56, which houses therein the rotor 48, the stator 49, the shaft 23, the connecting shaft 40 (which protrudes from one end of the box 56), the mechanical transmission 30 (i.e. the gears 36 and 37 and the freewheel 32) and the connecting shaft 50 engine with the Oldham coupling 51. The box 56 directly supports the stator 49, while the shaft 23 is supported by means of bearing 57 (which directly supports the rotor 48 and the connecting shaft 40, the latter by means of the bearings 58), and supports the components of the mechanical transmission 30 by means of bearings 59. The box 56 of the electric machine 8 is made of metal and is fixed (typically screwed) to the box 24 of the gearbox 10 to constitute a single part with the box 24 itself; when the box 56 of the electric machine 8 is fixed to the box 24 of the gearbox 10, the connecting shaft 40 and the primary shaft 15 are joined to one another by means of the coupling 41, and the activating shaft 27 and the connecting shaft 50 are joined to one another by means of the Oldham coupling 51.

The above-described transmission 7 has many advantages.

Firstly, the above-described transmission 7 is simple and cost-effective to make, particularly starting from an existing transmission which was not created for hybrid applications, because the general structure of the gearbox 10, and in particular the position of the pumps 25 and 26 of the gearbox 10, is not modified; in essence, starting from an existing transmission, which was not created for hybrid applications, the only interventions which must be carried out are the extension of the primary shaft 15 and of the activating shaft 27, the insertion of the freewheels 31 and 32 and the insertion of the mechanical transmission 30.

Furthermore, in case of electric traction (i.e. when the thermal engine 5 is off) the above-described transmission 7, the clutches 17 and 18 may be opened because the pumps 25 and 26 of the gearbox 10 are rotated by means of the mechanical transmission 30.

Finally, the above-described transmission 7 is particularly efficient from the energy point of view, because when the thermal engine 5 is off, the mechanical energy absorbed by the pumps 25 and 26 of the gearbox 10 is taken directly by the drive shaft 6 of the thermal engine 5 without any type of electromechanical conversion.

As shown in FIG. 6, the cooling and lubrication circuit 55, which circulates oil 60 in the rotor 48 and the stator 49 having the function of cooling the rotor 48 and the stator 49, is present inside the box 56 of the electric machine 8; it is worth noting that the oil 60 has good dielectric features, so as to be electrically insulating and thus avoid the formation of short-circuits through the oil 60 itself. Furthermore, the cooling circuit and lubrication circuit circulates oil 60 in the bearings 57, 58 and 59, having in this case the function of lubricating the bearings 57, 58 and 59 themselves.

The cooling and lubrication circuit 55 comprises a collection sump 61 of the oil 60, which is defined within the box 56 and in the lower part of the box 56 itself. The collection sump 61 has the function of collecting the oil 60, which by gravity drips downwards into the box 56, and thus constitutes a tank of the oil 60 itself. In essence, the cooling and lubrication circuit 55 has a “dry sump” type structure, in which the oil 60 is cyclically collected by gravity in the collection sump 61 defined in the lower part of the box 56.

The cooling and lubrication circuit 55 comprises an annular cooling chamber 62, which develops circularly about the rotation axis 39 (i.e. about the connecting shaft 40) and is arranged by the side of the stator 49 of the electric machine 8 on the side of the stator 49 facing the gearbox 10 (i.e. the cooling chamber 62 is interposed between the gearbox 10 and the stator 49). Some cooling nozzles 63 (only three of which are shown in FIG. 6) originate from an upper portion of the cooling chamber 62, which nozzles receive pressurized oil 60 from the cooling chamber 62 and address a jet of atomized oil 60 towards the stator 49 of the electric machine 8; in other words, by virtue of the action of the cooling nozzles 63 of the stator 49 (and partially also the rotor 48, which is next to the stator 49) is constantly invested by an oil mist 60. Between the stator 49 of the electric machine 8 and the wall of the box 56 cooling channels 64 are defined (only one of which is shown in FIG. 6) which are arranged axially in the upper part of the stator 49 and have the function of feeding the oil 60 “fired” by the cooling nozzles 63 along the entire outer cylindrical surface of the stator 49.

The cooling and lubrication circuit 55 comprises a distribution channel 65, which is obtained in central position inside the connecting shaft 40. The distribution channel 65 has a central oil inlet opening 60 on one end of the connecting shaft 40 and a plurality of outlet holes 66, which are arranged radially and are obtained crossing the connecting shaft 40 to lead from the connecting shaft 40 itself to the bearings 57 and 58, of the connecting device 38, and of the gear 36.

As shown in FIG. 7, the cooling and lubrication circuit 55 comprises a distribution channel 67, which is similar to the distribution channel 65 and is obtained in central position inside the connecting shaft 50. The distribution channel 67 has a central oil inlet opening 60 on one end of the connecting shaft 40 and a plurality of outlet holes 68, which are arranged radially and are obtained crossing the connecting shaft 50 to lead from the connecting shaft 50 itself at the bearings 59, the freewheel 32 and the gear 37.

As shown in FIG. 6, the cooling and lubrication circuit 55 comprises a radiator 69, typically of the air-oil type, by means of which the oil is constantly cooled by a flow of air normally generated by the advancement of the car 1. The radiator 69 receives pressurized oil 60 from the circulation pump 54, which in turn draws oil 60 from the bottom of the collection sump 61; from an outlet of the radiator 69, the pressurized oil 60 is fed to an annular feeding chamber, to the distribution channel 64 of the connecting shaft 40, and to the distribution channel 67 of the connecting shaft 50.

The operation of the cooling and lubrication circuit 55 is described with reference to FIGS. 6 and 7. In use, the circulation pump 54 draws oil 60 from the bottom of the collection sump 61 and feeds the pressurized oil 60 through the radiator 69, and thus to the annular cooling chamber 62, to the distribution channel 64 of the connecting shaft 40, and to the distribution channel 67 of the connecting shaft 50.

Oil 60, which reaches inside the cooling chamber 62, has the function of cooling this zone (and thus removing heat from this zone) to avoid the head from the gearbox 10 from overheating the electric machine 8. In other words, the heat from the gearbox 10 is “shielded” by the cooling chamber 62 (which, as previously mentioned, is arranged between the gearbox 10 and the electric machine 8) to avoid that heat from reaching the electric machine 8. Furthermore, the oil 60 which reaches the cooling chamber 62 is sprayed by the cooling nozzles 63 towards the stator 49 of the electric machine 8 (and therefore, inevitably, also towards the rotor 48, which is arranged in proximity to the stator 49) to directly cool down the stator 49 (and also the rotor 48); to increase and uniform the cooling of the stator 49, the oil 60 which is sprayed by the cooling nozzles 63 towards the stator 49 partially also flows along the axial cooling channel 64.

It is worth noting that the cooling nozzles 63 are mainly concentrated in an upper portion of the cooling chamber 62 (indicatively in an upper half of the cooling chamber 62), because the lower part of the stator 49 is immersed in the oil bath 60 contained in the collection sump 61; furthermore, the oil 60 which is sprayed by the cooling nozzles 63 of the upper portion of the cooling chamber 62 descends (i.e. goes towards the collection sump 61) by gravity and thus continuously invests the lower portion of the stator 49 (and thus, inevitably also the rotor 48, which is arranged in proximity to the stator 49).

According to the embodiment shown in FIG. 6, a single annular cooling chamber 62 is provided arranged by the side of the stator 49 of the electric machine 8 in the side of the stator 49 facing towards the gearbox (as previously mentioned, the main function of the cooling chamber is to “shield” the heat coming from the gearbox 10). According to a different embodiment (not shown), two symmetrically identical annular cooling chambers 62 (i.e. both provided with respective cooling nozzles 63, arranged on opposite sides of the stator 49) are provided.

The pressurized oil 60, which is fed into the distribution channels 65 and 67 of the connecting shafts 40 and 50, exits from the output holes 66 and 68 by its own pressure, and by centrifuge effect and thus lubricates the bearings 57, 58 and 59, the connecting device 38, the gears 36 and 37 and the freewheel 32. In this manner, all rotating mechanical parts are lubricated with oil guaranteeing a better lubrication and, above all, constant over time (on the contrary, a grease lubrication looses efficacy over time due to the progressive aging of the grease, which tends to dry up): consequently, the above-described electric machine has a very long working life, without need for maintenance interventions (except for, possibly, changing the oil 60, which is a simple, quick operation).

As shown in FIG. 11, the accumulation system comprises two reciprocal twin, independent battery arrays 70, which are connected to one another in series. Furthermore, the accumulation system 14 comprises, for each battery array 70, a respective electronic or electromechanical bypass switch 71, which is connected in parallel to the battery array 70 to form a bypass in the battery array 70; in case of failure to a battery array 70, the battery array 70 itself is cut off by closing the respective bypass switch 71 and the accumulation system 14 continues to work with the other battery array 70 only.

The accumulation system 14 is connected to the electronic power converter 13 by means of an electronic or electromagnetic bipolar switch 72. The electronic power converter 13 is provided with a two-way DC-DC converter of the “Buck-Boost” type, which has the function of modifying the voltage to electrically connect the accumulation system 14, which works at medium voltage (typically 200 Volts when both battery arrays 70 are operative) and the electronic power converter 13 that works at high voltage (typically 650 Volts). Furthermore, the electronic power converter 13 comprises a three-phase inverter 74, which on direct current side is connected to the two-way converter 73 and on the alternating current side is connected to the three-phase bars 75. A capacitor is connected in parallel between the converter 73 and the inverter 74 having the function of reducing the oscillations of the voltage and a (high value) resistor having the function of discharging the capacitor when the circuit is not used to avoid voltage remaining in the circuit for a long time dangerous for technicians carrying out maintenance/repair operations.

The electric machine 8 is connected to the three-phase bars 75 by means of an electronic or electromechanical three-phase switch 76. Furthermore, the three-phase bars 75 are connected to a three-phase connector 77 (i.e. provided with three terminals connected to the three three-phase bars 75 respectively) and a one-phase connector 78 (i.e. provided with two terminals connected to one two of the three three-phase bars 75, respectively).

The accumulation system 14 is also connected to a one-way DC-DC converter 79 of the “Buck” type, which also has the function of supplying a 12 Volt output voltage. The output of the one-way conveyor 79 is connected to a battery 80 of the vehicle 1 and thus an electric system 81 of the vehicle 1 running at 12 Volt. The one-way converter 79 can supply the energy necessary for operation to the electric system 81 of the vehicle 1 and keeps the battery 80 of the vehicle 1 charged.

A control unit 82 is provided, which has the function of superintending the operation of all electric systems controlling the bypass switches 71 and the separation switches 72 and 76, driving the converters 73 and 79 and piloting the inverter 74.

Normally, both battery arrays 70 are active and reciprocally connected in series to output a voltage of 200 Volts from the accumulation system 14 (each battery array 70 has at its terminal a voltage of 100 Volt). In case of fault in a battery array 70, the battery array 70 itself is cut off by closing the bypass respective switch 71 and the direct accumulation system 14 keeps working only with the other battery array 70; therefore, a voltage which is half nominal value (100 Volt instead of 200 Volt) is output from accumulation system 14 and such halving of the voltage is compensated by appropriately piloting the converters 73 and 79 so that the nominal voltage equal to 650 Volt is always present at converter output 73 and the nominal voltage of 12 Volt is always present at the converter output 79.

When the vehicle 1 is running, the separation switch 76 is closed so that the inverter 74 can pilot the electric machine 8 either as motor or as generator.

When the vehicle 1 is stationary, the separation switch 76 is open and the accumulation system 14 can be recharged by connecting the three-phase bars 75 to the electric network either by means of the three-phase connector 77 or by means of a one-phase connector 78; all three branches of the inverter 74 are active when the three-phase connector 77 is used, while only two of the three branches of the inverter 74 are active when the one-phase connector 78 is used. While recharging from the electric mains, the inverter 74 and the converter 73 are piloted so that the input mains alternating voltage (normally 220 V between phase and ground and 380 Volt between two phases) is transformed into direct 200 Volts at the terminals of the accumulation system 15 (100 Volts, if one of the two battery arrays 70 has been cut off by means of the respective bypass switch 71). 

The invention claimed is:
 1. A transmission for a road vehicle with hybrid propulsion; the transmission comprising: a gearbox with at least one primary shaft, at least one secondary shaft and at least one pump actuated by an activating shaft; at least one clutch connected to the primary shaft and including a part which is normally transmissive and is selectively connectable to a drive shaft of a thermal engine; at least one reversible electric machine including a shaft which is mechanically connectable to the primary shaft; a first mechanical transmission which transmits the motion from the normally transmissive part of the clutch to the activating shaft and is provided with a first freewheel to transmit the motion only when it rotates in a first rotation direction; and a second mechanical transmission which transmits the motion from the shaft of the electric machine to the activating shaft and is provided with a second freewheel to transmit the motion only when it rotates in a second rotation direction which is opposite to the first rotation direction of the first freewheel; wherein a gear ratio determined by the first mechanical transmission is higher than a further gear ratio determined by the second mechanical transmission, so that, given an equal input speed, the first mechanical transmission is to rotate the activating shaft faster than the second mechanical transmission does.
 2. The transmission according to claim 1, wherein the transmission comprises a disengagement sleeve, which is located along the activating shaft and upstream of the second mechanical transmission and is to allow the portion of the activating shaft arranged on the right of the disengagement sleeve to slide axially with respect to the portion of the activating shaft arranged on the left of the disengagement sleeve.
 3. The transmission according to claim 1, wherein the first mechanical transmission includes a cascade of gears and comprises a first gear, connected to the normally transmissive part of the clutch, and a second gear, which meshes with the first gear, is connected to the activating shaft, and comprises the first freewheel.
 4. The transmission according to claim 1, wherein the second mechanical transmission includes a cascade of gears and comprises a third gear, connected to the shaft of the electric machine, and a fourth gear, which meshes with the third gear, is connected to the activating shaft, and comprises the second freewheel.
 5. The transmission according to claim 4, wherein a rotor of the electric machine directly supports the third gear of the second mechanical transmission; the third gear is cup shaped, protrudes swing from one side of the rotor and has external teeth so as to mesh with the teeth of the fourth gear.
 6. The transmission according to claim 1 and comprising electronically controllable connecting device to mechanically connect the shaft of the electric machine to the primary shaft of the gearbox and electronically controllable to connect or disconnect the two shafts; with the second mechanical transmission connected mechanically to the shaft of the electric machine.
 7. The transmission according to claim 6, wherein the connecting device is located downstream of the second mechanic transmission relatively to the electric machine.
 8. The transmission according to claim 6, wherein the shaft of the electric machine has a tubular shape and has a central passing cavity; inside the central passing cavity of the shaft of the electric machine a first connecting shaft is located; the first connecting shaft is an extension of the primary shaft of the gearbox to which the first connecting shaft is butt jointed; the first connecting shaft crosses side to side the whole shaft of the electric machine and on the part opposite to the primary shaft connectable to the shaft through the connecting device.
 9. The transmission according to claim 8, wherein the connecting device comprises a first gear with straight teeth united to the first connecting shaft, a second gear with straight teeth united to the shaft, placed parallel and facing the first gear, a movable toothed sleeve mounted axially, and an electromagnetic actuating device that is aimed at axially moving the sleeve between a decoupling position and a coupling position, in which the sleeve engages with both gears so as to make the gears united angularly with each other.
 10. The transmission according to claim 9 and comprising a first encoder to detect in real time the angular position of the first connecting shaft and a second encoder to detect in real time the angular position of the shaft of the electric machine; by using the measurements provided by the two encoders the electric machine is controllable to synchronize the rotation of the two gears of the connecting device.
 11. The transmission according to claim 8 and comprising a second connecting shaft which on one side is connected to the second freewheel and on the other side is butt joint to the activating shaft.
 12. The transmission according to claim 8, wherein the second mechanic transmission includes a cascade of gears and comprises a third gear connected to the shaft of the electric machine and a fourth gear that engages with the third gear and is connected to the activating shaft; a rotor of the electric machine directly supports the third gear of the second mechanic transmission which is cup-shaped, protrudes cantilevered from one side of the rotor, and has external teeth so as to mesh with the teeth of the fourth gear.
 13. The transmission according to claim 12, wherein the crown of the third gear supports a cup-shaped element protruding cantilevered from one side of the third gear and is coupled to a second encoder to detect in real time the angular position of the shaft of the electric machine.
 14. The transmission according to claim 12 and comprising a circuit for cooling and lubrication of the electric machine to circulate oil and, the circuit including a circulation pump to receive the motion from the third gear.
 15. The transmission according to claim 8 and comprising a box of the electric machine which houses inside the electrical machine, the first connecting shaft, the connecting device, and the second mechanical transmission; the box of the electric machine separable and independent from a box of the gearbox and attached to the box of the gearbox to form one unity with the box of the gearbox.
 16. A transmission for a road vehicle with hybrid propulsion, the transmission comprising: a gearbox with at least one primary shaft, at least one secondary shaft and at least one pump actuated by an activating shaft; at least one clutch connected to the primary shaft and including a part that is normally conductive and is selectively connectable to a drive shaft of a thermal engine; at least one reversible electric machine including a shaft which is mechanically connectable to the primary shaft; a first mechanical transmission which transmits the motion from the normally conductive part of the clutch to the activating shaft and is provided with a first freewheel to transmit the motion when it rotates in a first rotation direction; and a second mechanical transmission which transmits the motion from the shaft of the electric machine to the activating shaft and is provided with a second freewheel to transmit the motion only when it rotates in a second rotation direction which is opposite to the first rotation direction of the first freewheel; wherein a gear ratio determined by the first mechanical transmission is higher than a further gear ratio determined by the second mechanical transmission, so that, given an equal input speed, the first mechanical transmission is to rotate the activating shaft faster than the second mechanical transmission does.
 17. The transmission according to claim 16, wherein the transmission comprises a disengagement sleeve, which is located along the activating shaft and upstream of the second mechanical transmission and is to allow the portion of the activating shaft arranged on the right of the disengagement sleeve to slide axially with respect to the portion of the activating shaft arranged on the left of the disengagement sleeve.
 18. The transmission according to claim 16, wherein the first mechanical transmission includes a cascade of gears and comprises a first gear, connected to the normally conductive part of the clutch, and a second gear, which meshes with the first gear, is connected to the activating shaft, and comprises the second gear.
 19. The transmission according to claim 16, wherein the second mechanical transmission includes a cascade of gears and comprises a third gear, connected to the shaft of the electric machine, and a fourth gear, which meshes with the third gear, is connected to the activating shaft, and comprises the second freewheel.
 20. The transmission according to claim 19, wherein a rotor of the electric machine directly supports the third gear of the second mechanical transmission; the third gear is cup shaped, protrudes swing from one side of the rotor and has external teeth so as to mesh with the teeth of the fourth gear. 